The invention relates to a power converter, in particular in the form of an inverter or a frequency converter.
In power converters, it is often necessary to detect a ground fault and/or short circuit at one or more terminals in order to establish a safe state, for example to interrupt a voltage or current output at the terminal in question, when a ground fault or short circuit is detected.
The invention is based on the object of providing a power converter comprising ground-fault and/or short-circuit identification which is simple to implement, cost-effective and/or space-saving.
The invention achieves this object by way of a power converter for driving a three-phase AC motor having three phase conductors, comprising: a first terminal for connecting a first of the three phase conductors of the three-phase AC motor, wherein a current which is to be output by way of the first terminal is routed to the first terminal by way of an electrical feed line; and a ground-fault and/or short-circuit identification circuit which is designed to detect a ground fault and/or short circuit of the first terminal, comprising: a coil having a winding which is arranged adjacent to the electrical feed line, wherein the winding does not surround the electrical feed line, and an evaluation device which is designed to evaluate a voltage, which is induced in the winding, for ground-fault and/or short-circuit identification. Embodiments of the invention are described and claimed herein.
The power converter, in particular a power converter in the form of an inverter or frequency converter, serves to drive a conventional three-phase AC motor which has, for example, one phase conductor or phase terminal for each phase. A respective phase conductor can form a so-called strand. Moreover, reference is also made to the relevant technical literature in this respect.
A power converter is understood to mean an apparatus for converting an electrical signal into another electrical signal, wherein, for example, a signal amplitude and/or a signal frequency is converted during the conversion process. This conversion is generally performed by means of electronic components, such as transistors, in particular in the form of IGBTs or MOSFETs, diodes or thyristors. Moreover, reference is also made to the relevant technical literature in this respect.
The power converter has a first terminal for connecting a first phase conductor of the three phase conductors of the three-phase AC motor or the associated terminal of the three-phase AC motor, wherein a current which is to be output or is output by means of (over) the first terminal is routed to the first terminal by means of an electrical feed line, for example in the form of an electrically conductive cable or a conductor track of a printed circuit board, within the power converter.
The power converter further has a ground-fault and/or short-circuit identification circuit which is designed to detect a ground fault and/or short circuit of the first terminal.
The ground-fault and/or short-circuit identification circuit has a coil with a winding. The winding is preferably arranged or positioned adjacent to the electrical feed line in such a way that a change in current in the electrical feed line induces a voltage, which can be measured by means of conventional components, in the coil or the winding of said coil. The winding is arranged in such a way that it does not physically surround or does not physically enclose the electrical feed line, in contrast to the principle of a conventional current transformer. In other words, the electrical feed line does not pass through the winding, as is the case in a conventional current transformer. Furthermore, the coil is not electrically looped-in between the first terminal and the electrical feed line. In addition, the first terminal preferably does not have an associated shunt resistor for current measurement.
The ground-fault and/or short-circuit identification circuit further has an evaluation device which is designed to evaluate a voltage, which is induced in the winding, for ground-fault and/or short-circuit identification. The evaluation device can have, for example, an evaluation electronics system or be embodied as an evaluation electronics system which generates a signal as soon as the induced voltage exceeds a threshold value which can be prespecified or is prespecified, that is to say a change in current, preferably an increase in current, in the electrical feed line exceeds an amount which can be prespecified.
The power converter can have a second terminal for connecting a second of the three phase conductors or the associated terminal of the three-phase AC motor, and a third terminal for connecting a third of the three phase conductors or the associated terminal of the three-phase AC motor.
Furthermore, the power converter can have a first current sensor, for example in the form of a conventional current transformer or a shunt resistor, which is designed to measure a current which is output at the second terminal.
Furthermore, the power converter can have a second current sensor, for example in the form of a conventional current transformer or a shunt resistor, which is designed to measure a current which is output at the third terminal.
The power converter preferably has precisely one ground-fault and/or short-circuit identification circuit and precisely two current sensors. In this way, conventional ground-fault and/or short-circuit identification can be carried out at the second and third terminals by means of the conventional current sensors. Ground-fault and/or short-circuit identification can be carried out by means of the ground-fault and/or short-circuit identification circuit at the first terminal in a highly space-saving and cost-effective manner in comparison to a conventional dedicated current sensor, without a conventional current sensor, for example in the form of a transformer, having to be provided for this purpose.
The winding or the turns can be formed by at least one winding-forming conductor track on a printed circuit board. The winding or the turns can be formed by conductor tracks on different layers of the printed circuit board, wherein, for example, in each case three turns of the winding can be provided on four layers, said three turns being electrically connected to one another, for example, by means of plated-through holes, so that a coil with a total of twelve turns is formed.
The electrical feed line can likewise be formed as one or more conductor tracks on the printed circuit board, wherein, for the purpose of electrical insulation between the electrical feed line and the winding, the electrical feed line can be arranged on one or more layers of the printed circuit board which are different from the layer or the layers on which the conductor tracks which form the winding of the coil are arranged.
The coil can be formed from a plurality of electrically coupled coil elements. By way of example, a first of the coil elements can be arranged on a first side of the electrical feed line, and a second of the coil elements can be arranged on a second side of the electrical feed line, which second side is situated opposite the first side.